High temperature under low light conditions suppresses anthocyanin biosynthesis in snapdragon petals associated with decreased sugar levels

•Anthocyanin accumulation was suppressed at high temperature under low light.•Sugar content in petals was decreased by high temperature under low light.•Expression of anthocyanin biosynthetic genes was suppressed by high temperature.•Sucrose treatment increased anthocyanin and sugar content at high temperature.•Sucrose treatment increased expression of AmCHS1, AmDFR, AmANS and AmUFGT. Anthocyanin accumulation of petals is suppressed at high temperatures. We therefore investigated the effects of temperature and light intensity on anthocyanin biosynthesis in snapdragons (Antirrhinum majus). Snapdragon plants were placed under four environmental conditions, combining two temperatures, 20°C /14°C (moderate temperature) and 36°C /36°C (high temperature) and two photosynthetic flux density (PPFD), 50 μmol m−2 s−1 (low light intensity) and 200 μmol m−2 s−1 (high light intensity), and held for 4 days. Pelargonigin-3-rutinoside was only found in petals as an anthocyanin. Anthocyanin accumulation associated with pigmentation of petals was suppressed at high temperature, and this suppression was enhanced under low light. Transcript levels of AmCHS1, AmCHI, AmF3H, AmDFR, AmANS and AmUFGT, which are involved in anthocyanin biosynthesis, in petals were significantly lower at the high temperature than at the moderate temperature. Sugar contents in petals also were significantly lower at the high temperature than at the moderate temperature. To clarify whether sugar is involved in suppression of pigmentation at a high temperature, cut flowers were treated with 0.15 M sucrose. Sucrose treatment increased anthocyanin accumulation, and the sugar content in the petals of cut flowers held at the high temperature. Sucrose treatment also significantly increased AmCHS1, AmF3H, AmDFR, AmANS and AmUFGT transcript levels in the petals at the high temperature. The results suggest that suppression of anthocyanin accumulation at high temperatures under low light is involved in the suppression of anthocyanin biosynthetic genes, which may be partially mediated with decreased sugar contents in petals.